The present invention relates generally to the field of aircraft communications, and more particularly to a system and method for providing voice call group functionality in a satellite based air traffic control system.
Air traffic control (ATC) systems control the airspace and airchannels between airports. Present day ATC systems utilize an air traffic communication infrastructure that has been in place since the 1950s. In the United States, this infrastructure includes more than 400 airport towers, 185 terminal radar approach control sites (Tracons), and 20 regional ATC centers. Voice communication between air traffic controllers and each aircraft remains, for the most part, entirely ground based. Airport towers communicate flight plans and instructions for take-off and landing to the aircraft while it is on the ground. Tracons monitor the aircraft and give flight instructions during take-off, approach and landing. Tracons typically monitor the aircraft up to 40 miles out of an airport in lower altitudes. Regional ATC centers take over control of the aircraft in high altitudes. Each regional ATC center maintains control over aircraft flying within its region, which may cover areas between 20 and 200 miles wide. As an aircraft enters or leaves the region of control of a regional ATC center, the regional ATC center communicates with either the Tracon site or the regional ATC center having control over the airspace from which the aircraft is entering or to which the aircraft is leaving to coordinate a hand-off of control of the aircraft. Tracon sites monitor aircraft within its airspace using airport surveillance radar (ASR), which typically has a range of approximately 55 nautical miles. Regional ATC centers monitor aircraft within their airspace using air route surveillance radar, which typically has a range of approximately 200 nautical miles.
Voice communication between air traffic controllers and aircraft is important for exchanging information such as route changes, weather and safety alerts, landing instructions, and information relating to crew or equipment emergency situations. Voice communication between a local airport control tower, a tracon site, or a regional ATC center and en route aircraft is provided in present day ATC systems using AM radio signaling. Typically, however, voice communication between a local airport control tower, a tracon site, or a regional ATC center ends when an aircraft leaves the airspace controlled by a respective ground control site. Thus, there is no seamless voice communication between a particular ground site and an airborne aircraft. Voice communication handoffs must be coordinated by the ground control site from whose airspace the aircraft is leaving and the ground control site into whose airspace the aircraft is entering. Handoffs are coordinated via ground line communications links such as ground telecommunications or microwave links.
Aircraft communication becomes even more complex when an aircraft crosses international borders. Each country or group of countries typically has its own ATC system and navigational infrastructure. This increases the complexity and therefore the reliability of ground-to-aircraft voice communication handoffs between different ATC systems. In addition, each ATC system may provide coverage of the entire country or group of countries, but more typically covers only a large part of it. Thus, some areas of some countries, and some areas between countries such as the airspace over oceans and the polar regions are uncovered. In uncovered areas, ground-to-aircraft communication may be slow and suffer more heavily from atmospheric interference, or may simply be unavailable.
Present day ATC communications systems have many disadvantages. First, present day ATC communications systems cannot provide seamless voice communication between a particular ATC tower, tracon or ATC center and an aircraft during the entire duration of its flight. Second, voice communication is not globally available. If an aircraft flies over an uncovered territory, all voice communication may be lost. Another disadvantage of current ATC communications systems is that radio communication signals over existing links are susceptible to atmospheric interference. Finally, because ATC systems are fragmented worldwide, a given aircraft does not maintain voice communication with any single ATC system during the entire duration of its flight.
Accordingly, a need exists for a method for maintaining voice communication between an aircraft and a ground air traffic control center for the entire duration of the aircraft's flight, if necessary, and thus independently of the location of the air traffic control center and the position of the aircraft. A need also exists for allowing a single air traffic controller or a pilot of an aircraft to simultaneously communicate with a group of pilots and or air traffic controllers.